For this section refer to the three Microphone Preamplifier module schematic pages (92-961) in Chapter 6.
Each of the five balanced microphone inputs feed a SSM2017. a precision surface-mount mi-crophone preamplifier IC. It unbalances and am-plifies the mic Signals up to -10 dEu. The preamp ICs are protected against Switching transients and DC voltage surges by the Zener diodes. resistors and coupling capacitors found between the input connector and the preamp IC.
DIP switch DS 1 has five switches to tum phan-tom power on or off to the five mic inputs. The switches ship from the factory set in the off posi-tion. Only those individual inputs that are power-ing condenser microphones should be set for phan-tom power on. The +45 volts is then coupled to the inputs via a pair of 6.81 k resistors.
Faceplate-accessible trimpots (RVI - RV5) set the preamp gain for a nominal output signal level of +4 dBu.
TPI - TP5 allow the internal nominal-lO dBu signal level to be monitored. Dual OP275 opamps boost and differentially balance the -10 dBu sig-nals to +4 dBu at the mic preamp output.
6-pin output connectors simplify connection to Input modules. paralleling the left and right chan-nels.
Polyswitch resettable fuses. Fl and F2. protect against board component short circuits. Once the over-current is removed. the fuses automatically reset. Test point TP6 is the -16 VDC check point.
TP9 is the + 16VDC check point. TP8 is the phan-tom supply check point. The ground reference test point is TP7.
P A C I F I C RESEARC H & E N G I N E E R I N G
INPUT MODULE
For this section refer to the two Input Module schematic pages (drawings 92-1004) and to the two SIM schematic pages (drawings 92-1001 and 92-1002) in Chapter 6.
AnalogSIM
The two identical balanced inputs (A and B) connect directly to the SIM socket. With an Ana-log SIM (99-1001) installed. the stereo audio sig-nals are unbalanced and amplified by OP275 dual differential opamps on the SIM card. Four single-pole Single-throw (SPST) solid-state analog switches toggle between the two inputs according to the faceplate A/B button selection.
The selected stereo input is then routed through trimpots R59 and R60 (Trim R and Trim L). The outputs of the trimpots go through buffer/ampli-fier U 4 before being converted into digital signals by U5. a Single chip ADC (Analog-to-Digital Con-verter). The ADC chip output (SDATA_SIM) is routed back to the Input PCA through the SIM socket.
DigitalSIM
With a Digital SIM installed (99-1002), the AES/EBU input is coupled to an AES/EBU Re-ceiver (U2) through an isolating transformer (T 1) and the A/B selection relay (K 1) .
U2 converts the incoming AES/EBU signal into a serial data signal (SDATA) with a separate left!
right clock (FSYNC) and serial clock (SCLK). In normal operation. the SDATA signal is routed through an Asynchronous SRC (Sample Rate Con-verter). U4. to synchronize the incoming digital audio with the DSP (via the FS64 clock). The out-put. SRC_DATA is then routed back to the Input module through the SIM socket as SDATA.
The SRC can be bypassed by physically jumpering El to E2. This switches which section of U 1 is active. Normally the odd pins couple the
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signals through to the output while the even pins are in a tri-state mode (at a high impedance). With El jumpered to E2. the IDCSDATA from AES/
EBU receiver U2 is connected directly to the In-put module via the even pins of U I, while the odd pins are at a high impedance.
If valid digital audio is not received. or if there are excessive errors (e.g .. loss of lock, parity er-rors. biphase encoding violation). an ERF (Error Flag) signal is sent back to the Input module where a NOR gate in U15 mutes the SDATA signal.
Input Module
Every Input module fader gets its reference volt-ages (both High and Low) from the DSP. Each fader's wiper output connects via a separate line to the DSP for individual channel level control.
The faceplate assignment switches (A/B select.
bus assignment. Cue. Off-Line) are all on a Single universal switch SIM. Each is a momentary SPST switch with an integral LED indicator. The switches connect directly to the gate array chip (FPGA. U14) while the LEDs on the switches are controlled by the FPGA through FET switches Q 1 - Q4, Q13 and Q14.
The module's On/Off switches mount on a sub-assembly (PR&E # 95-969-1). Each switch is a momentary SPST with incandescent lamps con-trolled by the FPGA through FETs Q5 - Q 12 and Q 15. The FETs not only turn the lamps on or off, they also generate an AC-like voltage to increase lamp life over normal DC powering.
When the Cue or Off-Line function is active. pre-fader controlled audio is applied to the appropri-ate summing bus. When any Program select but-ton is active. fader-controlled audio for that chan-nel is then connected to the selected digital Pro-gram bus.
The ten-position Logic Settings DIP switch (DS 1) is used to tell the FPGA whether logic con-trol is to be active on the A or B input along with
P A C I F I C R E S E A R C H & E N G I N E B R I N G
what type of logic signals to use. Either the A or the B input can be selected to use the logic control features in the standard module. With the optional B Logic Interface (PR&E # 99-1003) installed, each input has its own logic control.
There are five logic control outputs and six logic control inputs on each logic interface (92-1004, page 2 of 2). All control inputs (U8 - U13) and outputs (Ul - U5) are optically coupled for isola-tion and to prevent ground loops. The control in-puts are also current limited by U16 - U21 (LM317 regulators) so that any external logic level, from +5 to +40 VDC, can be accommodated.
Polyswitch resettable fuses, Fl - F4, protect the +12, +5, -16 and +16VDC supply against short circuit damage by board problems. TP I, TP2, TP3 and TP4 are available for checking the +12, +5, + 16 and -16 volt supplies after the poly fuses.
TELCO INPUT/OUTPUT MODULE Refer to the two Telco Input/Output Module schematic pages (92-1005) in Chapter 6.
The Telco Input/Output module is an optional module. Up to two of the modules can be installed into one mainframe in dedicated positions next to the Monitor module.
A Single Telco module must be installed in the first position to the left of the Monitor module. A second Telco module can be installed next to the first Telco module. This position automatically con-figures the second module as "Caller 2," while the first Telco module remains as "Caller I."
Each Telco module handles interfacing one tele-phone hybrid. All of the caller mix-minus audio control and caller audio program assignment is built into the module.
The balanced From Hybrid input (shown on page 1 of the schematic) is unbalanced and gain controlled through the two halves of opamp U1.
The hybrid input gain is set by faceplate trim pot, RVI (FROM HYBRID GAINTRIM).
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The output of the second half of the opamp con-nects to: U15 (an ADC, Analog-to-Digital Con-verter), to the left channel of the To Tape and Aux outputs (through buffer/balancing opamps U2, U9 and U 1 0), and is coupled through the motherboard to the other Telco module (as CALLER_OUT).
The ADC, U15, outputs digital data (SDATA) to the DSP through the motherboard connector.
The digital audio data is handled as in the Input modules, being converted back into analog on the Output module as required for the Cue, mix-mi-nus and analog program outputs.
The fader, like those on the Input modules, also connects directly to the DSP board, controlling the audio level in the digital domain.
The output assignment switchboard plugs into a SIM socket (see page 2 of the schematic). Each assignment switch is a momentary type with an LED indicator driven by FETs QlO - Q15. The module On and Off switch assembly plugs into the main PCA. The two switches are momentary SPST with incandescent lamp illumination driven by FETs Q1 - Q9.
The To Hybrid audio output (U3, U13, U14) carries a sum of the Telco mix-minus (TEL1_MM) and the caller's audio from the other Telco mod-ule (CALLER_IN), if one is installed.
TheTelco mix-minus audio (TELl_MM) comes from a DAC (Digital-to-Analog Converter) on the Output module. It is buffered by one-half of opamp U3 on the Telco module. In addition to going to the To Hybrid output, TELl_MM also goes to the right channel Tape/ Aux output through U2, U 11 and U12.
The CALLER_IN audio (from the other Telco module) may also be summed with TEL LMM follOWing the setting of a DIP switch. The DIP switch controls whether U 5 switches CALLER_IN to the left or to the right channel of the Tape/ Auxl Monitor outputs.
P A C I F I C R E S E A R C H & E N G I N E E R I N G
Revision A • 3/99